A Synovial joint, also known as a diathrosis, is a common and movable type of joint in the body. Synovial joints achieve movement at the point of contact of the articulating bones. A synovial joint is a part of the body where two adjacent bones are coupled and encapsulated within a synovial membrane, wherein the presence of synovial fluid within those capsules provides lubrication. More specifically, the joints have cartilage which coats the ends of the bones to allow for motion between the two bones without significant friction. Arthritis of a joint, which may arise from a variety of causes, is a debilitating condition that involves wear of the cartilage in a joint resulting in pain, stiffness, and loss of function. Treatment options for arthritis vary depending on the type of arthritis and include orthopedic bracing, medications, and joint replacement surgery, among other treatment options.
Joint replacement surgery is an orthopedic procedure that is performed on patients with various forms of arthritis to relieve pain, increase functionality, and improve quality of life. The joint replacement procedure may be performed, for example, on a knee, hip, or shoulder. However, there is about a 1-2% risk of infection in these joint replacements according to relevant literature. In fact, infections can be quite devastating for the patient and would require a surgical washout, followed by long-term intravenous antibiotics over a period of at least six (6) weeks. Chronic infections or infections by treatment-resistant bacteria entail a much more complex and invasive procedure. The surgeon must surgically remove all joint replacement parts. Then, an antibiotic loaded spacer, which makes the joint replacement less functional, is required. Finally, the patient must be treated with intravenous antibiotics for at least six (6) weeks. Once the infection is eradicated, the patient would need another surgical procedure requiring the use of a generally more complex joint replacement part.
Over the years, various pharmaceutical drugs have been developed to assist in the treatment of a wide variety of ailments and diseases. In many instances, however, these pharmaceutical drugs are not capable of being administered either orally or intravenously without substantial risk and detrimental side effects. Therefore, due to these risks and side effects that certain drugs impose, researchers have developed systems for administering these drugs to facilitate treatment of these ailments and diseases. Many of these systems provide for the pharmaceutical delivery device to release the pharmaceutical drugs at a certain rate in order to reduce the occurrence of detrimental side effects. Furthermore, in many therapeutic programs, in order to achieve the desired physiological or pharmacological effect, the pharmaceutical drugs must be administered by the pharmaceutical delivery system and released into the body at a controlled rate and over a prolonged period of time. In fact, in many instances, the rate of release of the drug from the pharmaceutical delivery device should have a zero order time dependence, that is, the rate of drug release is independent of time.
One embodiment of such a pharmaceutical delivery device is an orally administered pill or capsule which contains a drug encapsulated within various layers of a composition that dissolves over a period of time in the digestive tract, thereby allowing gradual or slow release of the drug into the system.
Another embodiment of such a delivery device is to mix a drug with a carrier material that is gradually broken down by body fluids. Therefore, as the carrier disintegrates, the pharmaceutical agent is released. Numerous materials, including waxes, oils, fats, soluble polymers, etc., have been used to serve as the carrier in such a pharmaceutical delivery device. While some of these delivery devices provide a delayed and prolonged release of the pharmaceutical drug, the desired constant rate of release over the extended period of time has not been obtained. One reason for variable rate of release is that as the carrier disintegrates, the surface area of the dosage unit decreases, concomitantly exposing increasingly smaller quantities of the carrier to the surrounding body fluids. This inherently results in a decline in the release rate of the pharmaceutical agent in the body over time.
Another type of device for controlling the administration of the pharmaceutical drugs is by coating the drug with a polymeric material permeable to the passage of the drug to obtain the desired effect. Such devices are particularly suitable for treating a patient when localization of the effect of the pharmaceutical agent is highly desirable, because the pharmaceutical agents can locally target only the designated area without having to expose the patient's entire body to the drug. Localizing the physiological and pharmacological effect of the pharmaceutical drug is advantageous, because any possible side effects of the drug could be minimized. These devices too, however, have inherent drawbacks. For example, a single material, such as silicone rubber polymers (especially polydimethylsiloxane), is generally selected to serve as the diffusion control membrane for the delivery device. These polymers were selected, in large part, because of their permeability to some important drug molecules. The mere high permeability without consideration for the release rate controlling properties, however, can be a significant disadvantage as to defeat the primary object of an acceptable drug delivery device. For example, with many important drug molecules, the diffusion rate through a polydimethylsiloxane membrane is very great, and, in fact, it is often greater than the rate of clearance of the diffused drug from the outer surface of the capsule. As a result, in many instances, the rate limiting step is the clearance of the pharmaceutical drug from the exterior of the capsule, rather than diffusion of the pharmaceutical drug through the capsule wall. As such, the pharmaceutical agent will not be released at the desired rate. Furthermore, clearance rate within the body is difficult to control, because the body is subject to frequent change. This inherently defeats the object of providing a drug delivery device which releases drug at a constant rate over a prolonged period of time.
Another type of device known to the art is to incorporate the pharmaceutical drug into certain type of liquid carriers, usually in microcapsule formulations. These microcapsules, however, are not designed for the controlled release of drugs for a prolonged period of time by using materials suitable for controlling the rate of release of the drugs. The microcapsules are frequently crushable, and they merely function as drug carriers supplying their drug in bulk. Therefore, rupture of the microcapsules results a bulk release rather than in a controlled release the pharmaceutical agents over time. As such, these types of capsules are not suitable for releasing drug at a controlled rate for a prolonged period of time.
The above described systems and devices are intended to provide sustained release rate of pharmaceutical drugs to bring about the desired local or systemic physiological or pharmacological effects. There are, however, many disadvantages associated with their use, including those discussed above. Furthermore, the drug may not be able to reach certain areas of the body via oral or intravenous administration of the drug. It will be appreciated by those versed in the art to which the present invention pertains that the present invention can be locally administered to target specified area as required.